The invention relates to a mechanical seal for sealing a rotating shaft and more particularly, to a mechanical seal having a leak detector for detecting leakage of process fluid from between a pair of relatively rotatable seal rings.
Mechanical face seals are used on various types of fluid handling devices or equipment, such as pumps and mixers. Such equipment has a rotating shaft and a process fluid chamber adjacent the shaft wherein the mechanical seal prevents leakage of fluid from the fluid chamber. Typically, such mechanical seals include a pair of adjacent seal rings which have opposing seal faces that define a sealing region radially therebetween to sealingly separate the fluid chamber from an exterior region. One of the seal rings is mounted on the shaft so as to rotate therewith while the other seal ring is non-rotatably mounted on a seal housing.
The seal rings may be provided in different combinations to define a single seal, double seal or tandem seal wherein in the double seals and tandem seals, multiple pairs of seal rings are provided. For example, U.S. Pat. No. 4,560,173 discloses double and tandem seals and U.S. Pat. No. 5,498,007 discloses a double seal. The disclosures of these patents are hereby incorporated by reference in their entirety.
In centrifugal pumps, mechanical seal failure is the most prevalent type of failure. In many services, a seal failure can even have catastrophic results. For example, flammable liquids are sealed in refinery applications and leakage of such process fluid can lead to fires that may cause significant loss of production and equipment as well as personal injuries.
In an effort to reduce the risk of failures, such as for light-hydrocarbon services, tandem mechanical seals may be provided wherein process fluid that leaks past a primary seal defined by a first pair of seal rings adjacent the process fluid chamber is contained by a secondary seal defined by a second pair of relatively rotatable seal rings. This leakage is then removed from a chamber defined between the primary and secondary seals before such leakage is able to migrate across the secondary seal and leak to the ambient environment.
However, end-users continue to use single mechanical seals, such as users in heavy-hydrocarbon services, since single mechanical seals are significantly less expensive. However, if leakage occurs in a single mechanical seal, such leakage is exposed to the ambient environment.
In an effort to identify leakage in single mechanical seals, end-users typically perform visual inspections whether through video cameras, which monitor pump installations, or through manual visual inspections of the seal. Further, pressure switches have been used to detect pressure increases in the gland of the mechanical seal although large leakage rates are required to produce detectable pressure increases. By the time a large amount of leakage is detected, the leakage still may have caused the failure of a shaft bearing associated with the mechanical seal which bearing failure can cause ignition of the fluid leakage.
In view of the foregoing, an object of the invention is to provide a mechanical seal having a leak detector arrangement, particularly in a single mechanical seal, which overcomes the disadvantages associated with known mechanical seals and procedures for detecting leakage therein.
In accord therewith, the invention relates to a mechanical seal having a leak detector associated therewith which readily detects leakage regardless of whether the mechanical seal is a single, double or tandem mechanical seal. In particular, the mechanical seal of the invention preferably relates to a single mechanical seal and the leak detector arrangement associated therewith.
In the seal arrangement of the invention, the mechanical seal includes a seal gland or housing in which the stationary seal ring is seated. A rotatable seal ring is mounted to a rotatable shaft so as to rotate therewith relative to the stationary seal ring. The gland surrounds the seal rings and also defines a chamber on the outboard side of the seal rings. The chamber in a single mechanical seal communicates with the ambient environment and in a double or tandem seal is disposed axially between a secondary set of seal rings. The gland further includes a conventional drain port wherein the leak detector assembly is connected to the drain port and thereby receives process fluid leaking past the seal rings.
The leak detector includes a detector housing having a collection chamber or reservoir, a drain orifice which allows a restricted flow of leakage out of the collection reservoir, and a fiber optic sensor which projects into the reservoir and detects the presence of liquid leakage.
In a first embodiment, the sensor detects a build-up of liquid in the leakage reservoir. In particular, the detector housing includes an inlet port in the side wall thereof wherein leakage flows into the reservoir sidewardly and then falls to the bottom of the reservoir at the restrictor orifice. If the flow rate of leakage into the reservoir is greater than the rate of outflow through the orifice, the leakage collects or builds up within the reservoir and eventually reaches the sensor that is located vertically above the orifice. The detection of fluid by the sensor indicates that the leakage has exceeded an acceptable flow rate, i.e. the outflow rate, thereby indicating impending or actual failure of the mechanical seal.
In a second embodiment, the inlet port of the detector housing is located at the top thereof while the tip of the sensor is located within the reservoir directly below the inlet port. The leakage flows into the reservoir through the inlet and drips onto the sensor tip whereby the sensor tip is able to count the drops striking the tip.
In a third embodiment, the sensor may be provided at the bottom of the reservoir housing directly adjacent to an outlet port that extends sidewardly through the housing side wall. This sensor operates similar to the second embodiment in that the sensor tip thereof is contacted by drops of leakage and thereby is used to count the rate of the drops which provides an indication of the leakage rate.
With these leakage detector arrangements, the flow rate of leakage can be detected. These leakage detectors are particularly suited for detecting low leakage rates so that leakage can be identified before a catastrophic failure condition is reached.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.